Relevance of host-derived and bacterial factors in Pseudomonas aeruginosa corneal infections.

Two pathogenic mechanisms of Pseudomonas aeruginosa corneal infections are discussed, one involving bacterial exoenzymes, the other involving polymorphonuclear leukocyte (PMN)-derived lysosomal enzymes. The objective of the present study was (1) to show the relative importance of the two mechanisms and (2) to evaluate the effect of active immunization against P. aeruginosa exoenzymes on ocular damage. Rabbits were immunized against P. aeruginosa alkaline protease (AP) or elastase (Ela) and challenged with the respective enzymes. Corneal damage was studied by light photography (LP). In another group, rabbits were immunized against AP, Ela and exotoxin A (ExoA) and challenged with P. aeruginosa strains PA01 or PA103. Corneal damage was studied with LP, light microscopy, and electron microscopy. Immunized animals were totally protected against intracorneal inoculation of P. aeruginosa proteases. Twelve hr and 24 hr after challenge with whole bacteria, immunized rabbits revealed less corneal damage than non-immunized animals. However, after 48 hr corneal damage (ie severe corneal ulceration) was comparable in both groups. The study suggests that corneal damage involving lysosomal enzymes from stimulated PMN is more important after bacterial infection than direct damage by P. aeruginosa exoenzymes.